a person will moove on a platform with a sensor that can detect his
movement and convert it to a mouse movement like on a computer
screen, so actually by the person movement on the platform we
can move a certain items on the screen. it should follow the person
movment speed and direction .

And you will need accompanying components (which are listed in the data sheet)

Obviously you will have to design it (I use WinQcad for schematic and PCB Design for large manufacturing. For cheap prototypes, Get ExpressPCB) and you will have to develop the firmware for the Microcontroller (see parallax site for compiler and developer). The firmware will have to output the communication signal the same way a mouse communicates. You may want to check the signal prior to the USB Driver...If you can't then...well, sorry.

The Mouse Driver on your PC is expecting specific data packets to come to it. You make your microcontroller spit out those same data packets, and your PC won't know the difference. All that you have to do once you get the data packets correct, is point your mouse driver START|Control Panel|System|Hardware|Device Manager|Mice and other pointing devices|and switch to a driver that will read the port you plug your device into.

I would help you out, but I am booked up with 2 projects right now. In another month or so, I can help...but Im not free